A nanosheet is a two-dimensional material having high anisotropic morphology with a thickness in the order of nanometers and width that is tens to more than several hundred times that value. Such a nanosheet not only inherits the functionality (conductivity, semiconductive properties, dielectric properties, and the like) of the parent phase, but also has a high specific surface area that is required for catalytic reactions and the like. Further, the nanosheet may exhibit unique properties such as one-dimensional quantum size effects. Furthermore, nanosheets can be used as functional building blocks to fabricate artificial superlattice nanostructures or three-dimensional architectures that cannot be achieved by conventional methods due to thermodynamic constraints, thus, the nanosheet potentially allows much more freedom in the control of properties and characteristics. Moreover, wet processing approaches can be utilized to fabricate such three dimensional nanostructures, which distinguishes nanosheet approach from typical physical deposition processes such as vapor phase synthesis, molecular beam epitaxy, etc. Such properties make nanosheets ideal for practical application including energy devices, from the viewpoints of not only performance but the processing route as well.
Proposed methods of nanosheet synthesis include methods which are induced via build-up from molecules, ions, and the like, and methods involving exfoliation of a layered compound into single layers. Such methods have been applied to achieve nanosheets composed of metal oxides and chalcogenides. Metallic nanosheets composed of a precious metal such as platinum or gold using a liquid phase reaction have also been proposed (refer to Patent Documents 1 and 2).
As a different approach for obtaining metallic nanosheets, the present inventors proposed technology that uses a layered metal oxide as a precursor (refer to Patent Document 3). This technology is a method for obtaining a metallic ruthenium nanosheet from a precursor by first preparing a ruthenium oxide with a nanosheet structure, and subsequent reduction to ruthenium nanosheet. A metallic ruthenium nanosheet film is obtained by reducing the ruthenium oxide nanosheet in a thin film state.